It seems with Lenin and the Bolsheviks setting up the Cheka, they had the same aim as the Okhrana; to root out any opposition. In what ways were they different?
You might be interested in some previous threads comparing the Cheka and the Okhrana:
Was the USSR's method of keeping order (especially under Stalin) similar to the old tsarist way? - 4 comments, over 1 year old.
The commenters here explore the goals of, methods used, and punishments inflicted by both organizations as well as the practices that were inherited by the NKVD.
How much of a stretch were the Cheka from the Okhrana? - 6 comments, over 2 years old.
Despite some terminological confusion, the commenters here contrast the scale of operations and powers available to both organizations as well as provide a variety of sources for followup reading.